1. Field of the Invention
This invention relates generally to the etching and passivation of polyimide layers having metallization thereon, and more particularly to a process which allows photoimageable material to be utilized as a mask to reveal the desired pattern to be etched on a substrate and the same material to be used as a mask during the etching and also following the etching as a passivation material overlying the remaining polyimide substrate with the metallization layers thereon. It finds particular use in processes in which tape automated bonding (TAB) materials are manufactured in strip form.
2. Description of the Prior Art
Polyimide substrates with metallization layers thereon have found many different uses in the semiconductor industry. One particular use is for providing tape automatic bonding (TAB) structures which are comprised of a long ribbon of material having metallization in the form of lines extending on one side, and more recently on both sides thereof, for providing electrical connection to chips. In the manufacture of such TAB products, it is necessary to expose the metallization at various locations on the strips of material and indeed have lines extend beyond edges of the material so as to provide contacts for connection to pads on semi-conductor chips. It is further necessary to provide some type of passivation or protection layer over the metallized layer remaining on the tape and which does not extend beyond the ends thereof to provide the necessary protection to the metallization from the environment.
In the past, the construction of these polyimide substrates with metallization thereon has been performed in a number of different ways.
Typically the polyimide would be provided with metallized lines thereon and the polyimide substrate and metallized lines would be covered with some type of photoresist material which was patterned to reveal the portions of the polyimide which is to be removed. Several different types of photoresist have been used for this patterning but they have suffered from certain serious drawbacks. First a photoresist must be strong enough to resist the etchant used for the polyimide material which is a concentrated potassium hydroxide at temperatures in excess of 70.degree. or 80.degree. C. The photoresist must be sufficiently resistant during the etching process to prevent the potassium hydroxide from attacking the polyimide except at the exposed areas.
The photoresists that have had this property have conventionally been those which required removal by chlorinated solvents which require special handling as opposed to those that can be removed by nonchlorinated solvents. Further, while these photoresist materials that have been used have held up reasonably well during the etching process, they have not had the adherent properties necessary to remain in place after the etching in a bonded relationship over the substrate and metallization thereon to provide the necessary passivation. Hence, after the etching has been performed, it has been necessary to then strip the remaining photoresist and perform a separate step of applying passivating material to the substrate with the lines thereon. This problem is further exacerbated if the exposed or extending copper lines have to be further processed such as by gold plating which entails the necessary surface preparation followed by the plating operation.
Examples of prior art etching methods of the underlying polyimides are shown in U.S. Pat. Nos. 4,436,583; 3,833,436; 4,523,976; and 4,606,998. These patents are illustrative of various types of etching processes utilizing KFTR and other types of photoresists and lift-off processes as well as dry etch processes and the use of Si02 which is patterned in certain types of operations involving other types of polyimide structures from those used for TAB. None of these patents disclose the process of the present invention.